There are so many different RTAs and sub tanks on the market these days that your best bet would be to search RTA or sub ohm tank on Youtube and watch some reviews. Search within the past 6-8 months for the newest options. I've heard a lot of good things about the current crop of mesh coils for sub tanks. If I were shopping for one, I would look for something that takes mesh coil heads.
RTAs are a whole other thing with a lot of different options in airflow, single or dual coil, etc. My favorite RTA at the moment is my Bravo by Wotofo. I like open airflow and dual coils, though. Watch some reviews.
For example...
My gunmetal Bravo RTA on a USV-L.